In an op-ed in the Wall Street Journal Marty Makary says that federal public health officials are overestimating the time it will take for the U. S. to achieve “herd immunity”:
Anthony Fauci has been saying that the country needs to vaccinate 70% to 85% of the population to reach herd immunity from Covid-19. But he inexplicably ignores natural immunity. If you account for previous infections, herd immunity is likely close at hand.
Data from the California Department of Public Health, released earlier this month, show that while only 8.7% of the state’s population has ever tested positive for Covid-19, at least 38.5% of the population has antibodies against the novel coronavirus. Those numbers are from Jan. 30 to Feb. 20. Adjusting for cases between now and then, and accounting for the amount of time it takes for the body to make antibodies, we can estimate that as many as half of Californians have natural immunity today.
The same report found that 45% of people in Los Angeles had Covid-19 antibodies. Again, the number can only be higher today. Between “half and two-thirds of our population has antibodies in it now,†due to Covid exposure or vaccination, Mayor Eric Garcetti said Sunday on “Face the Nation.†That would explain why cases in Los Angeles are down 95% in the past 11 weeks and the positivity rate among those tested is now 1.7%.
Undercounting or removing the many Americans with natural immunity from any tally of herd immunity is a scientific error of omission. When people wonder why President Biden talks about limiting Fourth of July gatherings, it’s because his most prominent medical adviser has dismissed the contribution of natural immunity, artificially extending the timeline.
which in turn motivated the question that is the title of this post. The honest answer is neither we nor the federal public officials nor, as far as I know, anyone else actually knows. What we do know is that about 8% of the population has been confirmed as having had COVID-19. There are significantly higher estimates of how many people have contracted the disease, for example, this one at News-Medical:
World health experts have long suspected that the incidence of COVID-19 has been higher than reported. Now, a machine-learning algorithm developed at UT Southwestern estimates that the number of COVID-19 cases in the U.S. since the pandemic began is nearly three times that of confirmed cases.
The algorithm, described in a study published today in PLOS ONE, provides daily updated estimates of total infections to date as well as how many people are currently infected across the U.S. and in 50 countries hardest hit by the pandemic.
As of Feb. 4, according to the model’s calculations, more than 71 million people in the U.S. – 21.5 percent of Americans – had contracted COVID-19. That compares with the substantially smaller 26.7 million publicly reported number of confirmed cases, says Jungsik Noh, Ph.D., a UT Southwestern assistant professor in the Lyda Hill Department of Bioinformatics and first author of the study.
but, that, too is just a guesstimate. I might have more confidence if I saw the actual algorithm used to produce the results. The true number (which has changed since I started writing this post) could be higher than that, lower than that, or about right.
Arguendo, let’s assume that the true number is something between 8% and 21.5%. Picking a number at random, let’s say 15%. How many of the remaining pool of 85% of the population would need to be vaccinated before herd immunity is achieved? We don’t know the answer to that, either:
The percentage of people who need to be immune in order to achieve herd immunity varies with each disease. For example, herd immunity against measles requires about 95% of a population to be vaccinated. The remaining 5% will be protected by the fact that measles will not spread among those who are vaccinated. For polio, the threshold is about 80%. The proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known. This is an important area of research and will likely vary according to the community, the vaccine, the populations prioritized for vaccination, and other factors.
Taking the pessimistic estimate of 95%, that would suggest that as many as 80% of the population would need to be vaccinated. Taking the most optimistic possible view based on present knowledge it suggests that the number would be between 55% and 72%. Clearly, it makes a difference.
I agree that no one knows when we will reach herd immunity. Different for each virus. What I do think we will reach well before July is the point where R will be less than 1 almost everywhere. At that point it is almost impossible to have large outbreaks.
Steve
I think herd immunity will be around 60%, but its hard to tell how much immunity is conveyed by infection or how long it lasts, so that aspect is hard for public health officials to include.
I notice that Illinois’ governor will end the emergency when 50% of adults have received at least one dose. That’s probably at the low-end of herd immunity.
Maybe there is data out there but I haven’t seen any info on how long the mRNA vaccines will protect individuals. Consequently, how long will herd immunity last?
@Andy, the only study I’ve seen is that there is strong memory response six months after infection, but that would be from natural infection. Not a lot of data for a new virus and new vaccines. Common colds caused by coronaviruses apparently reinfect an average of every eight years, either because of waning immunity or antigenic drift. Not a lot of studies of common colds though. But even if reinfected every eight years, one’s immune system might be sufficient to prevent serious disease.
The NYT reports that as of 3/25 there had been 30.1 million cases and 546,000 deaths in the US. I suppose that is confirmed, reported cases. Since the great majority of people get what amounts to a bad flu, and likely don’t seek medical care. The true number must be higher. 70 million seems credible; maybe even 100 million. On the other hand, we know that anyone who dies with a measurable covid titre is labelled a covid death regardless of cause of death, so the death total is inflated.
However, after a year, only 9% of the US population is confirmed to have caught covid, and less than 0.2% have died from it. That hardly seems like a pandemic worth of the mass hysteria we have seen. It certainly isn’t polio, which I remember, or German measles or diphtheria…
Herd immunity is one of those undefined and undefinable terms that pseudo-experts like Fauci like to throw around. I have to think that after a full year of pandemic we have run out of susceptibles and actually have “herd immunity” right now.
It is also pretty clear that you can expect about 10% of the population to catch any epidemic disease, and that is really the upper bound. The Black Death killed around 30% to 60% of Europeans, and that is the worst plague for which we have any kind of data. The early plagues during the Roman Empire might have been as bad, and might even have been the same disease.
I think the question is framed all wrong.
The discussion presumes a static percentage — which itself makes a series of assumptions
1) Peoples behavior won’t change depending on their perception of risk. It is evident people engage in more risky behavior when they feel less risk; that implies the required percentage is higher as “normality” is restored.
2) No seasonality — it is quite evident that the virus spreads much faster in a “wintry” climate then a “summer” one. Herd immunity looks much easier in summer then in winter.
3) The virus not evolving — SARS-COV2 is not behaving like measles or smallpox; where the virulence and resistance to natural immunity or vaccines didn’t change over decades to centuries. Instead it seems more similar to influenza, where vaccine efficiency can shift by 30%, and virulence can change by 50% in a single year.
It is really quite plausible we’ll hit what seems like “herd immunity” for a few months this summer followed by we need to vaccinate 80% of the population for a new variant in the fall.
PS; I would discount natural infections as a good defense to re-infection against variants; evidence from Brazil, South Africa, and in-vivo lab results show it is ineffective. The best bet is to take a vaccine; and even then a booster may still be required.
Good observations all, CuriousOnlooker. I think the most honest answer to all of the questions you’re raising is we don’t really know. We don’t know how long natural resistance will persist or whether it will apply to the variants. We don’t know how long the resistance produced by the vaccines will persist or whether it will apply to the variants. We don’t know if boosters will be necessary or even effective.
We also don’t know whether there will be long term effects from the mRNA-based vaccines or what they might be.
I remain with the belief that I have held now for more than a year: we’re going to need to learn to live with the risks COVID-19 brings with it. Shutting down in the hope that it will go away is unlikely to be a formula for success.